Scanning probe microscopes (SPMs) are designed to sense one or more physical properties of a surface at a high degree of resolution in order to provide a detailed analysis of the topographical or other properties of a surface. Using scanning probe microscopy, it is possible to detect physical features on the scale of individual atoms and molecules. Among the physical properties which SPMs can image are attractive and repulsive forces due to interatomic forces, electrical potentials, magnetic forces, capacitive forces, and conductive, optical and thermal properties. In addition to detecting physical properties of a surface, SPMs can be used in a variety of applications including the imaging and processing of semiconductors, magnetic materials and storage media, biological materials, polymers, coatings, metals and the like. SPMs are also used in surface science, materials science, crystal growth, electrochemistry and other studies of surfaces. SPM imaging may be perform in ambient, liquid and vacuum environments.
In general, SPMs include a probe which is positioned in very close proximity to a sample surface in order to detect one or more of the above topographic or physical properties of the surface. For example, in scanning force microscopes (SFM), also commonly referred to as atomic force microscopes (AFM), the probe includes a tip which projects from the end of a cantilever and is used to detect interatomic forces between the probe tip and the sample. Typically, the tip is very sharp in order to achieve maximum lateral resolution by confining the force interaction to the end of the tip. A detection system is used to detect the deflection of the cantilever in order to determine the contours of the surface property being probed. In scanning tunneling microscopes (STM), the probe includes a sharp conductive needle-like tip which is used to measure tunneling current flowing between the tip and a conducting or semiconducting sample surface. In STMs, the tip is typically positioned only a few Angstroms above the surface being probed.
The scanning operation of an SPM is performed by a fine x,y,z stage, or scanner. The scanner typically moves the sample or probe in the x-y plane such that the probe follows a raster-type path over the surface to be analyzed. In many SPMs, the scanning movement is generated with a piezoelectric tube. The base of the tube is fixed, while the other end, which may be connected to either the probe or the sample, is free to move both laterally and as vertically input voltage signals are applied to the piezoelectric tube. The use of a piezoelectric tube in this application is well known and is described, for example, in an article by Binnig and Smith, Rev. Sci. Instrum., 57 1688 (1986). An SPM may be operated under feedback control, whereby a feedback controller maintains a constant separation between the probe and sample during a scan by adjusting the z position of the z scanning stage.
A key issue common to all SPMs is the accurate positioning and movement of the probe relative to the sample surface in the x, y and z directions. Movement of the probe and sample relative to each other may be performed by moving the probe, the sample or both the probe and sample. A need exists for SPMs which provide highly accurate scanning in the x, y and z direction. One significant problem in this regard is cross coupling between different scan directions. A need therefore exists for a scanning mechanism which enables the probe and sample to be scanned relative to each other with minimal cross coupling.
The ability to optically view a probe and/or sample before during or after scanning probe microscopy is an important feature of an SPM. Optical viewing facilitates a variety of functions associated with scanning probe microscopy including, for example, coarse adjustment of separation between the probe and the sample, coarse adjustment of the sample position laterally relative to the probe, manipulation of the sample without having to remove the sample or disassemble the instrument and alignment of the cantilever deflection detection system. A need therefore exists for an SPM which is designed to provide enhanced optical viewing of the sample and/or probe in an SPM including the capability to perform optical imaging using the various optical modes of an optical microscope. These and other objectives are provided by the present invention.